Comparing two files in linux terminal

Question

There are two files called \"a.txt\" and \"b.txt\" both have a list of words. Now I want to check which words are extra in \"a.txt\

Answer 1

Use comm -13 (requires sorted files):

$ cat file1
one
two
three

$ cat file2
one
two
three
four

$ comm -13 <(sort file1) <(sort file2)
four